1. Field of the Invention
This invention relates generally to the drilling of wells for the production of petroleum products from subsurface zones of interest and to drilling activities for multilateral branches that extend from a primary wellbore to a zone or zones of interest located laterally from the primary wellbore. More particularly, the present invention is directed to a survey method and apparatus to record the position and the orientation of locating devices in a string of well casing, and to recognize the type of matching profile of the locating and orienting device that has been installed in the casing string at a specific well depth, to thus enable lateral branch operations such as casing window milling, lateral branch drilling, lateral branch entry, completion, and treating, to be accomplished simply and efficiently from the primary wellbore.
2. Description of the Related Art
In order to drill lateral branches in an oil and gas well, some side-tracking methods may use a permanent locating and orienting device that is built into the casing. Typically an indexing coupling is connected between sections of casing and defines an internal landing profile allowing a well tool having a matching internal landing profile to be landed and latched therein. For the purpose of indexing, the indexing coupling can also define an internal orienting slot having an azimuth that is known. A lateral branch well tool having an orienting key located within the orienting slot will therefore be oriented with respect to the azimuth of the internal orienting slot. Such a permanent indexing coupling allows positioning and orienting accurately and consistently any equipment that is needed to build and/or complete a lateral branch or conduct other azimuth specific operations within the well. This technique is disclosed in U.S. patent application Ser. No. 08/937,032, filed on Sep. 24, 1997, which is incorporated herein by reference.
Typically, sections of well casing are connected by threaded couplings so that the relative rotational positions of adjacent casing sections can vary significantly. The same is true with respect to indexing couplings which are typically connected to adjacent casing sections by threaded joints. To achieve precision location of indexing couplings within casing strings for wells of significant depth, according to conventional practices, the location and orientation of each joint of the casing string relative to adjacent joints must be precisely measured. Additionally, other parameters that control casing positioning, casing stretch for example, must be carefully monitored and controlled as the casing is being positioned and cemented within the wellbore so that the indexing coupling will be located precisely at the desired depth and the indexing slot of the indexing coupling will be precisely located at a preselected azimuth. As the many casing sections of a well are connected, minor errors at a number of casing joints can accumulate, thus positioning the orienting slot of any particular indexing coupling at an azimuth that is significantly different from the azimuth that is intended. Thus azimuth specific subsurface operations conducted from the reference of the indexing slot of the indexing coupling can have a significant error. Moreover, when the casing cementing operation has been completed the position of the well casing will be permanent, thus any error of casing positioning will interfere permanently with lateral branch operations.
Obviously, when exceptionally close monitoring and recording is being done during casing installation to ensure that actual indexing coupling positioning and orientation precisely matches the casing installation plan, the cost of the casing installation procedure, as compared to casing installation without such monitoring, is significantly increased, thus adversely influencing the overall cost of the well drilling and completion procedure. It is desirable therefore to provide a procedure for installing well casing having indexing couplings located therein so that the well casing can be installed without the need for precision azimuth controlled orientation of the indexing couplings relative to the earth formation. It is also desirable to provide a procedure for efficiently and accurately identifying the specific azimuth orientation of each of the orienting couplings of a casing string after the casing string has been run into the wellbore and cemented. This feature will permit the well tools to be landed therein to be selectively oriented with respect to the precisely measured existing azimuth of the orienting slot of the indexing coupling so that intended well operations, the drilling of lateral branches, well completion activities, well treating, casing window milling, digital imaging, as examples, can be carried out from an azimuth reference and coupling orientation that have been precisely measured and recorded by a well log.
When a well casing is installed, landing and indexing nipples, also referred to herein as indexing couplings are frequently connected in the casing string at selected depths to enable well tools to be run through the casing and landed and latched to the internal profile of the indexing coupling. At times the internal profiles of several indexing couplings of a casing string will be intentionally different so that only a well tool having a matching landing profile can be landed and latched therein. This feature enables well tools to be run through the casing string and through non-matching indexing couplings until an indexing coupling having a matching profile has been reached. The landing nipple with a matching profile will allow the locking dogs of the tool to seat within the matching profile and establish a latching connection therewith.
Under circumstances where an existing well having indexing couplings, particularly indexing couplings having an orienting slot therein, are encountered and the internal profile and indexing geometry and orientation are not known, it is desirable to provide a system for creating an image of the internal geometry of the indexing coupling on a well log and referencing the image to local deviation and rotation, i.e., the inclination of the well casing and indexing coupling and the angle of rotation, measured from an azimuth of reference such as magnetic north. The image so created should display the positioning and orienting features of the indexing coupling, i.e., the precise internal profile of the indexing coupling and the azimuth and dimension of its indexing slot so that azimuth specific lateral branch operations may be efficiently designed and conducted from the reference of the indexing slot.
It is therefore desirable to provide a logging system having an ultrasonic scanner to thus provide the capability of creating an image accurately identifying the internal geometry of the indexing coupling or other positioning or indexing device. It is also desirable to provide a logging system having the capability of correlating the image of the internal geometry of the selected indexing coupling in terms of local references in the downhole environment. This will enable various azimuth specific downhole operations to be designed with the known internal geometry and orientation of a selected indexing coupling in mind.